Need to add support for managing credentials used by pipelines

[dchassin]

Some pipelines require credential to function. There is no mechanism in either CLI and openfido-client to manage those credentials locally.

Recommend the following:

1. Add openfido credential PRODUCT {add,delete} FILENAME.
2. Copy the credential file to the pipeline input folder after the input files are loaded (so they cannot be downloaded).
3. Add a Upload credentials to the Settings dialog. Dialog layout:

Product   Credential file    
--------   --------------
Weather   credentials.csv   [Trashcan Icon]

In general credentials files should be structured as CSV, e.g., credentials.csv:

KEY1,VALUE1
KEY2,VALUE2
...

or as JSON, e.g., credentials.json

{
  "KEY1" : "VALUE1",
  "KEY2" : "VALUE2",
  ...
}

where the key provided depends on the credential implementation in the pipeline, e.g. username,MYNAME, password,MYPWD, etc. For example, the weather pipeline needs APIKEY and EMAIL. These should be delivered as environment variables exported to the shell that runs openfido.sh, e.g., export OPENFIDO_SECRET_APIKEY="MYAPIKEY" and export OPENFIDO_SECRET_EMAIL="my.email@example.com" so they can be used in the script.